Rare cloud cover over Antarctica

Some of the coldest temperatures on Earth have fostered a rare cloud formation over Australia's Mawson station in Antarctica, scientists said on Tuesday.

Some of the coldest temperatures on Earth have fostered a rare cloud formation over Australia's Mawson station in Antarctica, scientists said on Tuesday. Meteorological officer Renae Baker captured spectacular images of the nacreous clouds, also known as polar stratospheric clouds, on July 25.

The clouds only occur at high polar latitudes in winter, requiring temperatures less than approximately minus 80 Celsius.

A weather balloon measured temperatures down to minus 87 Celsius on the day the photos were taken. "Amazingly, the winds at this height were blowing at nearly 230 kilometres per hour," Baker said on the Australian government's Antarctic division's website.

Reflecting like an airborne mother-of-pearl shell, the cloud colours are produced when fading light at sunset passes through water-ice crystals blown along a strong jet of stratospheric air more than 10 kilometres above the ground.

Australian Antarctic Division atmospheric scientist Andrew Klekociuk said the clouds were seldom seen but could have long-ranging effects. "These clouds are more than just a curiosity," he said.

"They reveal extreme conditions in the atmosphere and promote chemical changes that lead to destruction of vital stratospheric ozone."